Spinach could be weapon against citrus scourge

By Christopher Sherman

Associated Press

Published: Friday, March 30 2012 12:00 a.m. MDT

Pete Timmer, professor emeritus at the University of Florida's Citrus Research and Education Center, was called a pessimist when he published an article two years ago on the future of that state's citrus industry. He predicted among other things that genetically enhanced citrus trees resistant to HLB would be widely available in 20 years, but by then there would be few small citrus growers left in the business.

Even with aggressive control of pysllids, Florida has struggled to get a handle on HLB because so many trees are infected, he said. The problem is compounded because young trees planted to replace those already infected are more vulnerable than mature trees.

"Once you get to 100 percent infection you're dead," Timmer said.

Mirkov was drawn to the spinach proteins because as part of the plant's innate immune system they shield it against a broad spectrum of threats. This sort of protein, known as a defensin, is found in plants, insects and mammals, he said.

The trees that will soon begin field testing represent two generations of Mirkov's research, each group carrying one of the two spinach genes. Those two generations of trees already spent 1½ years in a greenhouse packed with psyllids in Florida that exposed them to a concentration of infected insects that far exceeds what they would experience in a commercial grove. Six distinct lines of trees emerged from the third generation with zero infection and about six lines from the second generation passed that test with 10 percent or less infection. Unmodified trees had nearly 100 percent infection rates.

"That pretty much sealed that we had something good," Mirkov said.

The two spinach genes are combined in each tree of a fourth generation that is undergoing psyllid house testing now and should outperform the others, Mirkov said.

That's the generation Mirkov and Southern Gardens Citrus hope to steer through the regulatory process, which could take three to four years and a variety of tests to prove the modified trees are safe for humans and the environment.

"We all want to see our research get used to solve real world problems, I mean that's why you do this stuff," said Mirkov. "I suppose there's some people that do science just for the sake of doing science, but my interest has always been let's find out things in the lab and then use it to solve a problem."

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